Input Power Control for Thermoelectric-Based Refrigerator Apparatuses

ABSTRACT

A refrigerator apparatus includes a housing with an interior chamber, a thermoelectric device that is thermally coupled to the interior chamber, a temperature sensing device that is thermally coupled to the interior chamber, the temperature sensing device providing a temperature measurement; and electronics configured to generate and apply input power to the thermoelectric device, and to adjust the input power maintaining a functional relationship between the input power and the temperature measurement.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No. ______entitled “Thermoelectric-Based Refrigerator Apparatuses” filed herewith.

TECHNICAL FIELD

The invention relates generally to refrigeration devices and, inparticular, to micro refrigerators.

BACKGROUND ART

Millions of people in the U.S. with diabetes depend on a reliable supplyof insulin. Although insulin can be readily purchased, and has areasonable shelf life, it needs to be stored under proper conditions.Insulin is a protein that can be degraded by exposure to excessive heator cold. In particular, even brief exposure to temperatures below 2° C.or above 30° C. can cause unacceptable degradation. In general, it isrecommended that insulin be stored in a refrigerator for extendedstorage, but room temperature storage for periods up to a month is alsoconsidered acceptable, provided that the room temperature does notexceed 30° C. (86° F.). Many insulin users are satisfied with keeping asupply in their refrigerator. However, refrigerators occasionally areset at a temperature too low for safe storage of insulin, and insulincan accidentally be frozen. In addition, insulin users who travelregularly are often faced with issues, such as hotel rooms that do notprovide refrigerators, and long airplane flights. During travel in suchunpredictable environments, it is possible that the insulin could beexposed to damaging temperatures, even without the knowledge of theowner.

The only devices currently on the market aimed at providing portablepersonal refrigerated insulin storage are phase-change devices. Theseare devices that contain a fluid/solid that melts near 10° C.; they areessentially ice packs. The fluid might be water, or some water-basedfluid. Like an ice pack, prior to use, they must be pre-chilled in afreezer. The heat of fusion absorbed as the solid melts is used to keepit cold for an extended period.

Several difficulties are encountered with these devices. Among these arethat temperature control is marginal; the device starts at freezertemperature (which is too low for safe insulin storage) and graduallywarms to the phase change temperature. The temperature then remainsfairly constant until all of the phase-change material melts, at whichtime the temperature begins to rise again. If the phase-change materialis water, the temperature plateau is at 0° C., which is again too coldfor long-term insulin storage. Phase-change materials can be found thatmelt at 10° C., but they do not have the high heat of fusion of water,limiting the lifetime of the device. Lifetime of the devices is alsolimited if the mass of the phase-change material is to be keptreasonable. In addition, there is no reliable indicator of when thesolid is nearly or completely exhausted. The user only knows it is timeto recharge the device when it begins to get too warm. Finally, the onlyway to recharge the device is to leave it in a freezer for some time;the user is then faced with the issues of finding a freezer, and ofwhere to keep the insulin while the storage device is being recharged(since it is not safe to leave the insulin in the device while it is inthe freezer).

It would be useful to be able to provide a portable refrigeration devicethat helps prevent unacceptable degradation of a substance storedtherein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a refrigerator apparatus according to anexample embodiment of the present invention;

FIG. 2A is a cross-sectional end view of the refrigerator apparatus ofFIG. 1, shown with its housing opened to provide access to the interiorchamber;

FIG. 2B is a cross-sectional side view of the refrigerator apparatus ofFIG. 1;

FIG. 2C is a cross-sectional top view of the refrigerator apparatus ofFIG. 1;

FIG. 3 shows an example embodiment of electronics for a refrigeratorapparatus, the electronics including a single cold side temperaturesensor;

FIG. 4 is a plot of thermoelectric voltage versus cold side temperatureaccording to an example operating mode where a substantially constantinput power is applied within a desired temperature range;

FIG. 5 is a plot of thermoelectric voltage versus cold side temperatureaccording to an example operating mode where a proportional input poweris applied within a desired temperature range;

FIG. 6 is a plot of normalized power versus temperature according to anexample operating mode where no input power is applied within a desiredtemperature range;

FIG. 7 shows an example embodiment of electronics for a refrigeratorapparatus, the electronics including both cold side and hot sidetemperature sensors;

FIG. 8 shows an example embodiment of electronics for a refrigeratorapparatus, the electronics including a Universal Serial Bus (USB)interface; and

FIG. 9 shows an example embodiment of electronics for a refrigeratorapparatus, the electronics including a USB interface and batterycharger.

DISCLOSURE OF INVENTION

The present invention involves refrigerator apparatuses, for example,portable micro refrigerators for insulin or other medicines, drugs andmaterials that require storage in a temperature controlled environment.

In example embodiments, refrigerator apparatuses are controlledaccording to one or more operating modes. In an example operating mode,the measured temperature of a substance stored in the refrigeratorapparatus is allowed to vary over some or all of the temperature rangeunder which the substance (e.g., insulin) can be safely stored withoutsignificant degradation. For refrigerator apparatuses that use batteriesas a power source, this and other operating modes described hereinincreases the lifetime of the battery.

Referring to FIG. 1, in an example embodiment, a refrigerator apparatus100 includes a housing 102. In this example embodiment, the housing 102includes a top portion 104 and a bottom portion 106. In this exampleembodiment, a hinge 108 mechanically couples the top portion 104 and thebottom portion 106, and a latch 110 secures the portions of the housingin a closed position as shown. It should be appreciated that othermechanisms can be used to secure the top portion 104 and the bottomportion 106 together.

In this example embodiment, the top portion 104 includes a display 112(e.g., LCD, touch screen), user input mechanisms 114 (such as a numerickeypad, arrow buttons, etc.), indicator lights 115 (e.g., LEDs), and aspeaker 117. In this example embodiment, the refrigerator apparatus 100also includes a wireless communications interface 116 (e.g., Bluetooth)and a wired communications interface 118 (e.g., USB). Other inputmechanisms, indicators, communications interfaces and/or combinations ofthese devices can also be employed. In this example embodiment, the topportion 104 and the bottom portion 106 are both provided with access tothe communications interfaces 116 and 118 (e.g., via a signal interfacesuch as a ribbon cable providing a communications link between the topportion 104 and the bottom portion 106).

Example embodiments are configured to permit programming of therefrigerator apparatus 100. In an example embodiment, one or more of thecommunications interfaces 116 and 118 are used to download executableprogram files and/or data (e.g., related to control modes for particularsubstances and particular environmental or other conditions). In anexample embodiment, the user input mechanisms 114 allow a clinician orother user of the refrigerator apparatus 100 to provide data inputsand/or navigate a Graphical User Interface (GUI) provided at the display112. In an example embodiment, one or more of the display 112, indicatorlights 115, and speaker 117 is used to provide an indication of acondition (e.g., associated with a measured temperature, temperaturehistory, state of battery charge, or operational status of a componentwithin the refrigerator apparatus 100), or to prompt the user to providea data input (e.g., make a decision regarding selection of an operatingmode), establish a remote communications link (e.g., to downloadsoftware updates), discard/replace a stored substance that may havebecome degraded, or to take some other recommended or required action.

For example, the refrigerator apparatus 100 can be configured(programmed) to monitor temperature extremes to which a stored substancehas been exposed, and notify the user (through the display 112,indicator lights 115 and speaker 117, for example) that the substancehas been exposed to unacceptable temperatures. Also by way of example,the refrigerator apparatus 100 can be programmed to monitor batteryvoltage and provide an indication (e.g., activate an alarm) when batterycapacity is running low.

Referring to FIGS. 2A-2C, in an example embodiment, the refrigeratorapparatus 100 includes an interior chamber 120 which is defined bychamber walls 122 of the top portion 104 and the bottom portion 106,respectively. The chamber walls 122, as well as the outer walls 123, aremade of aluminum, for example, or any material(s) with good thermalconductivity. In an example embodiment, the interior chamber 120 iscomplementary in shape to a container 125 in which a substance isstored. In an example embodiment, inner surfaces 124 of the chamberwalls 122 are semi-circular in shape as shown.

In this example embodiment, the refrigerator apparatus 100 includesinsulators 126 (e.g., aerogel insulators) and thermoelectric devices 128adjacent to the chamber walls 122 of each housing portion as shown. Theinsulators 126 control the heat load on the cold side of thethermoelectric devices 128. Each of the housing portions also includeselectronics 130 (e.g., an electronics module) and batteries 132 forproviding input power.

In an example embodiment, a refrigerator apparatus includes a housingwith an interior chamber, an aerogel insulator within the housing, athermoelectric device that is thermally coupled to the interior chamber,and electronics configured to generate and apply input power to thethermoelectric device. In an example embodiment, the aerogel insulatoris molded. In an example embodiment, the aerogel insulator includeslayers of aerogel fabric. In an example embodiment, the aerogelinsulator is under a vacuum.

In an example embodiment, the interior chamber 120 is configured toprovide a data input to the electronics 130 that identifies thesubstance within the container 125. In this example, an ID reader 134 isprovided within the interior chamber 120. By way of example, the IDreader 134 is complementary in shape to a base portion of the container125. This facilitates proper seating of the container 125 so thatmachine-readable indicia or the like (e.g., a bar code) carried on thebase portion of the container 125 can be read, thereby providing anidentification of a substance within the container 125. Thisidentification data is in turn provided to the electronics 130 which, inexample embodiments, are configured to automatically select particularoperating modes or other temperature control schemes that are customizedto the particular needs of the identified substance.

In the illustrated example embodiment, the two halves (top portion 104and bottom portion 106) are completely independent in power supply andcooling elements, providing redundancy. In an example embodiment, thethermoelectric devices 128 are controlled by their respectiveelectronics 130 to pump heat from the chamber walls (cold cell) 122 tothe outer walls (case) 123. In an example embodiment, the case is madeof a good thermal conductor (such as aluminum) and is large enough todissipate the heat without noticeable temperature rise. In theillustrated example embodiment, power is supplied to each of the twohalves (top portion 104 and bottom portion 106) by two pairs ofbatteries 132 (e.g., AA batteries). The batteries 132 can be, but arenot required to be, rechargeable batteries. In an example embodiment,the electronics 130 controls the power to maintain the desiredtemperature on the cold side.

In an example embodiment, a refrigerator apparatus includes a housingwith an interior chamber, thermoelectric devices that are thermallycoupled to the interior chamber, and dual redundant electronicsconfigured to generate and apply input power to the thermoelectricdevices. In an example embodiment, the dual redundant electronics areconfigured to maintain for each of the thermoelectric devices afunctional relationship between the input power and a temperaturemeasurement. In an example embodiment, the dual redundant electronicsinclude dual microcontrollers each configured for direct connection to abattery without the use of a voltage regulator.

FIG. 3 shows an example embodiment of electronics 300 for a refrigeratorapparatus. In this example embodiment, the electronics 300 include abattery pack 302, microcontroller 304, power converter 306,thermoelectric 308, thermistor 310, power source 320, power distributionand conditioning circuit 322, battery charger 324, and communicationsinterface 330 configured as shown. Switch SW is a single pole, doublethrow switch that connects the circuitry to either the battery pack 302or the output of the power distribution and conditioning circuit 322.The microcontroller 304 monitors a temperature sensor, the thermisor Rtin this example embodiment, and calculates an appropriate operatingvoltage for the thermoelectric 308. In this example embodiment, ananalog voltage is generated using 4 digital outputs (DO 0 through DO 3)and a resistor divider network (R1 through R5). Other techniques such aslow-pass filtering of a high-frequency pulse-width modulated digitaloutput can be used to provide an analog output voltage using feweroutput ports and components, or direct digital output can be used with apower converter designed for digital inputs. In this example embodiment,the power converter 306 is an analog power converter which acts as animpedance-matching amplifier to drive the thermoelectric cooler.Microcontrollers have high-impedance digital outputs whilethermoelectric coolers tend to be low-impedance devices. The powerconverter 306 provides unity gain or some other fixed gain as required.

In an example embodiment, the thermistor 310 is part of a resistordivider with R6. When the DO 4 digital output is driven high, currentflows through the thermistor and R6. The voltage of the thermistor-R6junction, read by analog input 0 (Ain 0) is a function of temperature.With appropriate choice of R6, the analog input voltage will beproportional to temperature. Use of a digital output to activate thethermistor circuit allows reduced energy consumption since temperaturemeasurements are not required continuously. The thermal time constantsare typically longer than a few seconds and the temperature can bemeasured by the microcontroller 304 within a tenth of a second.

In an example embodiment, the electronics 300 include a single cold sidetemperature sensor (the thermistor 310). It should be appreciated,however, that temperature sensors other than thermistors can also beused.

An additional energy conservation approach is the direct connection ofmicrocontrollers to batteries without the use of a voltage regulator. Byway of example, a pair of 1.5-V alkaline batteries, connected in series,produces an output voltage between 0 and 3.0 Volts, depending on thestate of discharge for the batteries. The output voltage for a pair ofbatteries that have been drained by 90% over the course of at least anhour is about 2.0 Volts. Current-generation microcontrollers are capableof operating over a 1.7-to-5 Volt supply range, and are thus capable ofoperating directly on batteries down to ˜10% of their remainingcapacity. Use of a voltage regulator to power the microcontroller wouldsuffer from a 10-to-20% energy loss due to conversion inefficiency, thusdecreasing available battery lifetime.

In an example embodiment, the microcontroller 304 and thermistor 310 arepowered directly by batteries and can operate over a 1.7-to-5V voltagerange while maintaining temperature measurement accuracy. Thissimplifies the circuitry by eliminating a second power converter thatwould normally be used to provide a stable supply voltage for themicrocontroller. It also extends battery life by eliminating powerconversion losses from this second converter.

In an example embodiment, a refrigerator apparatus includes a housingwith an interior chamber, a thermoelectric device that is thermallycoupled to the interior chamber, and electronics configured to generateand apply input power to the thermoelectric device, the electronicsincluding a microcontroller configured for direct connection to abattery without the use of a voltage regulator.

In an example embodiment, the electronics 300 allow a refrigeratorapparatus to operate on external power, power source 320, such as a walloutlet, or through such sources as cigarette lighters or aircraft powersources. In an example embodiment, the power source 320 is a solar cell.By way of example, a solar cell powered embodiment using body-mountedcells and rechargeable batteries accommodates long-term operation awayfrom civilization, e.g., camping or ground shipping of medicines. In anexample embodiment, the solar power is monitored and divided betweencooling and battery charging as needed. In the example embodiment shownin FIG. 3, the power distribution and conditioning circuit 322 monitorspower output by the power source 320 and distributes power between thetemperature control circuitry (the microcontroller 304 and the powerconverter 306) and the battery charger 324.

In an example embodiment, the refrigerator apparatus can be recharged byexchanging batteries, which takes only seconds. Alternatively, therefrigerator apparatus can be recharged in any wall outlet or otherconvenient power source, such as a cigarette lighter in a car. At thesame time, the refrigerator apparatus continues to function as acontrolled refrigerator while being recharged. In either case, whetherpowered by disposable or rechargeable batteries, the substance (e.g.,insulin) can be left in the refrigerator apparatus at all times.

The microcontroller 304 can be programmed to implement additional powerconservation features such as transitioning the microcontroller 304 to asleep state or sleep mode, and turning off the temperature measurementcircuit when not needed.

In an example embodiment, one or more input/output (I/O) pins of themicrocontroller 304 are connected to the communications interface 330,which can include one or more wireless or wired communicationsmechanisms. In an example embodiment, the microcontroller 304 alsoincludes I/O connections from the ID reader 134 (denoted “ID READER”)and to an indicator device, e.g., the display 112, indicator lights 115,and/or speaker 117 (denoted “INDICATOR DEVICE”).

In an example embodiment, the microcontroller 304 includes a memorydevice for storing executable and other program files, as well as datafiles (e.g., substance-specific temperature control profiles, monitoredtemperatures and voltages), and user inputs and preferences.Alternately, the memory device is separate from the microcontroller 304,e.g., as part of the electronics 300 and/or remotely located andaccessed via the communications link 330. Distributed processingconfigurations can also be employed.

In an example embodiment, the microcontroller 304 is programmable and isconfigured (programmed) to monitor the temperature of a substance storedin the refrigerator apparatus and to control the power applied to thethermoelectric device. The microcontroller 304 can be programmed via thecommunications interface 330. Additionally, in this example embodiment,user inputs to the microcontroller 304 are provided using one or more ofthe display 112 (e.g., a touch screen) and the user input mechanisms114.

In an example embodiment, a refrigerator apparatus includes a housingwith an interior chamber, a thermoelectric device that is thermallycoupled to the interior chamber, a temperature sensing device that isthermally coupled to the interior chamber, the temperature sensingdevice providing a temperature measurement, an indicator device (e.g., adisplay, light, and/or speaker), and electronics configured to generateand apply input power to the thermoelectric device. The electronics areconfigured to monitor the temperature measurement, compare thetemperature measurement to a range of acceptable temperatures for asubstance stored within the interior chamber, and to control theindicator device to provide an indication of exposure to an unacceptabletemperature when the temperature measurement is outside the range ofacceptable temperatures.

In an example embodiment, the electronics are configured to track thetemperature measurement over time. In an example embodiment, theelectronics are configured to provide the indication when thetemperature measurement has been outside the range of acceptabletemperatures for an unacceptable amount of time for the substance. Forexample, as a safety feature, in any operating mode, the refrigeratorapparatus can be programmed to monitor the temperature extremes of thestored substance, and provide a notice, alarm, indication, or the like(through the display 112, indicator lights 115, and/or speaker 117, forexample) that the substance has been exposed to unacceptabletemperatures. In an example embodiment, the electronics are configuredto apply the input power depending upon an expected lifetime of thesubstance.

FIG. 4 is a plot of thermoelectric voltage versus cold side temperatureaccording to an example operating mode where a substantially constantinput power (denoted “PLATEAU”) is applied within a desired temperaturerange. In this range, the thermoelectric voltage applied (in thisexample, 0.5V) matches the thermal heat load to the cold side. In thisexample operating mode, at colder temperatures, the thermoelectricvoltage is proportionally reduced as shown (denoted “WARMING”) to allownormal thermal heat loads to warm the cold side. If the cold sidetemperature approaches a dangerously cold condition such as freezing fora substance that should not be frozen, the thermoelectric voltage can gonegative, thus pumping heat from the outside into the interior. Athigher temperatures, thermoelectric cooling is proportionally increasedas shown (denoted “REDUCED COOLING”) to drop temperatures into thedesired range. At still higher temperatures, the maximum thermoelectricvoltage (denoted “MAXIMUM COOLING”) is reached. In some instances, thislimit is either imposed by battery voltage or by the electronics. Inother example embodiments, power is applied to either cool or heat evenwhen the cold side temperature is within the desired temperature range,e.g., a non-zero thermoelectric voltage is applied in the PLATEAUregion. For example, an external temperature measurement or other inputcan be processed to determine an adjustment (e.g., offset and/or gain)in the thermoelectric voltage or other modification to thethermoelectric voltage profile for that particular operating mode.

The proportional temperature control schemes described herein canprovide increased efficiency and longer battery life than simple on/offcycling of the thermoelectric. This is due to the nonlinear coolingefficiency of a given thermoelectric as a function of input power. Theproportional control approach also minimizes thermal cycling within thethermoelectric cooler that can lead to premature failure.

Thermoelectric devices are solid-state heat pumps. They take advantageof the Peltier effect, in which heat is either evolved or absorbed atthe junction of two dissimilar electrical conductors when an electriccurrent flows through the junction. In a Peltier cooler, the rate ofheat absorption is linearly proportional to the electric current and thedifference between the Peltier coefficients of the two conductors. Thus,increasing the current increases the rate of heat pumping. The currentcannot be increased without penalty, however, because the conductorsused to form the Peltier junction also have an electrical resistance,and the current flow through the conductors will generate resistiveheating. This heating is proportional to the square of the electriccurrent. At high currents, therefore, the resistive heating willoverwhelm the Peltier cooling and the device will cease to function as arefrigerator.

A consequence of the linear relation between current and Peltier coolingand the quadratic relation between current and resistive heating is thatit is preferable to operate a Peltier cooler with a proportional powercontrol. Normal refrigerators, operating on a fluid-dynamic cycle,typically operate with a thermostatically-controlled on-off cycle; whenthe thermostat detects that the cold zone is warmer than a set point,full power is applied to the cooling unit. When the temperature fallsbelow the set point, the cooling unit is turned off. If the same controlscheme is applied to a thermoelectric device, there will be significantinefficiencies in the system. For example, if the average duty cycle ofthe cooling element is 50%, the current flow during the time that poweris on is twice what it would need to be to deliver the same amount ofcooling in a continuous manner. Doubling the current will quadruple theresistive heating. The 50% duty cycle will reduce this by a factor oftwo, so the net increase in resistive heating relative to thesteady-state case will be a factor of two. Similarly, if the duty cycleis only 10%, the resistive heating is ten times higher than it wouldhave been in the steady state case. Thus, the most efficient way tooperate the cooling elements is with a proportional power control systemwhere the power applied to the cooling elements is just enough tomaintain the temperature at the set point.

FIG. 5 is a plot of thermoelectric voltage versus cold side temperatureaccording to an example operating mode where a proportional input power(denoted “SLOPE”) is applied within a desired temperature range. In thisexample, the functional relationship between the thermoelectric voltageand the cold side temperature proportionally changes as shown butremains linear within the desired temperature range. In otherembodiments, the functional relationship between the thermoelectricvoltage and a measured temperature can include proportionalrelationship(s) and/or non-proportional relationship(s). In otherembodiments, the functional relationship is between input power and ameasured temperature (or a temperature differential). In still otherembodiments, the functional relationship can include discontinuities(i.e., steps) in the thermoelectric voltage (or applied power).

In other embodiments, the microcontroller 304 is programmed to receiveuser inputs that may override application of power according to aparticular operating mode. For example, the boundaries of a desiredtemperature range can be changed. In other embodiments, only authorizedusers (such as clinicians) can provide such overriding inputs.

FIG. 6 is a plot of normalized power versus temperature according to anexample operating mode where no input power is applied within a desiredtemperature range. This operating mode provides an extended range ofconditions (in this example, from 5° C. to 20° C.) under which no poweris applied. The applied power for any operating mode described hereincan be a function of a measured temperature, measured temperatures, atemperature differential, battery voltage, user inputs, and/or othermeasurements, inputs, data, etc.

As noted previously, the function does not need to be linear. In anexample embodiment, a curve with more gentle transitions between regionsis provided. When the temperature is in the acceptable range and isstable, there is no need to apply power. As the temperature goes outsidethis range, the power is gradually increased (either heating or cooling)to attempt to keep the measured temperature in the correct range. In anexample embodiment, maximum power is applied only if the temperaturegoes beyond a limit where the stored substance is subject to (rapid)degradation.

In an example embodiment, a refrigerator apparatus includes a housingwith an interior chamber, a thermoelectric device that is thermallycoupled to the interior chamber, a temperature sensing device that isthermally coupled to the interior chamber, the temperature sensingdevice providing a temperature measurement, and electronics configuredto generate and apply input power to the thermoelectric device, and toadjust the input power maintaining a functional relationship between theinput power and the temperature measurement. In an example embodiment,the functional relationship includes a proportional relationship betweenthe input power and the temperature measurement. In an exampleembodiment, the input power is adjusted to maintain the functionalrelationship when the temperature measurement falls outside a range ofacceptable temperatures for a substance stored within the interiorchamber. In an example embodiment, the input power is adjusted tomaintain the functional relationship when the temperature measurementfalls inside a range of acceptable temperatures for a substance storedwithin the interior chamber. In an example embodiment, the input poweris held substantially constant when the temperature measurement fallsinside a range of acceptable temperatures for a substance stored withinthe interior chamber. In an example embodiment, no input power isapplied when the temperature measurement falls inside a range ofacceptable temperatures for a substance stored within the interiorchamber. In an example embodiment, the electronics are configured toapply the input power to cause the thermoelectric device to heat theinterior chamber only when the temperature measurement indicates adangerously cold condition for a substance stored in the interiorchamber. In an example embodiment, the electronics are configured toapply the input power to cause the thermoelectric device to cool theinterior chamber at a maximum available cooling rate of thethermoelectric device only when the temperature measurement indicates adangerously hot condition for a substance stored in the interiorchamber. In an example embodiment, the temperature sensing device is athermistor circuit, and the electronics include a microcontroller thatprovides a digital output to activate the thermistor circuit.

An operating mode can be custom tailored to a particular substance,insulin for example. Since insulin can be safely stored for extendedperiods at temperatures up to 30° C., in an example embodiment, a safetybackup operating mode is employed. In normal use, the refrigeratorapparatus continuously monitors the temperature of the insulin bottle.When the refrigerator apparatus is in an environment where thetemperature is below 30° C., no power is applied to cooling the insulin.When the temperature of the environment rises above 30° C., the powercontrol circuit senses the temperature and applies power to thethermoelectrics to maintain the temperature below 30° C. Since peoplerarely spend extended periods in environments with temperatures above30° C., the long-term drain on the batteries is limited. For people whoprefer to store their insulin at lower temperatures, the temperaturesetting of the refrigerator apparatus can be adjusted to any desiredvalue.

In another example operating mode, the insulin is stored in therefrigerator apparatus which is, in turn, stored in a cold environmentsuch as inside a standard refrigerator. If the refrigerator setting istoo low, the refrigerator apparatus, being thermoelectric, can operatein reverse as a heater, ensuring that the insulin bottle is not exposedto unacceptably low temperatures.

In another example operating mode, the refrigerator apparatus monitorsinsulin temperature, external temperatures, and battery voltage anddetermines an optimum strategy to maximize insulin lifetime (e.g., keepas cool as possible as long as the temperature is above 2° C.) for afixed operational time (e.g., 24 hours) based on an initial batterycapacity (e.g., 2-AA alkaline cells). This mode accommodates users whoare uncomfortable with room-temperature insulin.

Additionally, refrigerator apparatuses described herein can be operatedin a long-term, wall-powered mode with any desired temperature setting.

In an example embodiment, a refrigerator apparatus includes a housingwith an interior chamber, a thermoelectric device that is thermallycoupled to the interior chamber, and a temperature sensing device thatis thermally coupled to the interior chamber, the temperature sensingdevice providing a temperature measurement, and electronics configuredto receive power from a battery and to generate and apply input power tothe thermoelectric device, and to adjust the input power according to anoperating mode selected by the electronics depending upon thetemperature measurement and a voltage measurement at an output of thebattery. In an example embodiment, the operating mode is selected by theelectronics to be a normal operating mode when the voltage measurementindicates a sufficiently high battery output voltage, and a low energyreserve operating mode otherwise. In an example embodiment, theelectronics, when adjusting the input power in the low energy reserveoperating mode, prevent the thermoelectric device from operating at themaximum heating or cooling rates of the thermoelectric device. In anexample embodiment, the operating mode includes a functionalrelationship between the input power and the temperature measurement.For example, the functional relationship includes a proportionalrelationship between the input power and the temperature measurement.For example, the input power is adjusted to maintain the functionalrelationship when the temperature measurement falls outside a range ofacceptable temperatures for a substance stored within the interiorchamber. For example, the input power is adjusted to maintain thefunctional relationship when the temperature measurement falls inside arange of acceptable temperatures for a substance stored within theinterior chamber. In an example embodiment, the input power is heldsubstantially constant when the temperature measurement falls inside arange of acceptable temperatures for a substance stored within theinterior chamber. In an example embodiment, the electronics areconfigured to apply the input power to cause the thermoelectric deviceto heat the interior chamber only when the temperature measurementindicates a dangerously cold condition for a substance stored in theinterior chamber. In an example embodiment, the electronics areconfigured to apply the input power to cause the thermoelectric deviceto cool the interior chamber at a maximum available cooling rate of thethermoelectric device only when the temperature measurement indicates adangerously hot condition for a substance stored in the interiorchamber.

When operating on battery power alone, the operating mode is oftendirected toward maximizing battery lifetime. This is governed by thetotal energy available in the batteries, the efficiency of the powercontrol system, the efficiency of the thermoelectric modules, and theheat load on the cold side. Both of the later two are functions of thehot side temperature, which is typically somewhere between roomtemperature and 40° C. In an example operating mode, whenever the roomtemperature is below 30° C., the only power requirement is for thetemperature monitoring function, which can be kept very low. Whentemperatures go above 30° C., the thermoelectrics cut in, drawingsignificant battery power. The efficiency of thermoelectric modules is astrong function of the temperature difference across the module.However, with temperature differences smaller than 10° C., theefficiency is very good. The heat load on the cold side can becontrolled with insulation.

Since the refrigerator apparatus can encounter a variety ofenvironments, the power required to maintain a stable cold-zonetemperature may vary. Various refrigerator apparatus embodiments providefor power control that is a function of both internal and externaltemperatures.

FIG. 7 shows an example embodiment of electronics 700 for a refrigeratorapparatus, the electronics including both cold side and hot sidetemperature sensors. The electronics 700 are the same as the electronics300, except as described differently below. In this example embodiment,the electronics 700 include a thermistor 312 which monitors the hot sideof the thermoelectric 308. In an alternative embodiment, the thermistor312 (or other temperature sensing device) is positioned to measure anexternal temperature. In this example embodiment, the microcontroller304 monitors two temperature sensors (Rt1 and Rt2 thermistors, in thisexample embodiment) and the voltage produced by the battery pack 302. Inthis example embodiment, temperature sensor Rt1 is thermally connectedto the cold side of the thermoelectric element while temperature sensorRt2 is thermally connected to the hot side. In an example embodiment,the microcontroller 304 measures both temperatures, estimates the energyleft in the battery pack 302 by measuring its output voltage, andcalculates an appropriate driving voltage for the thermoelectric 308.

In an example embodiment, a refrigerator apparatus includes a housingwith an interior chamber, a thermoelectric device that is thermallycoupled to the interior chamber, temperature sensing devices thatprovide temperature measurements, and electronics configured to generateand apply input power to the thermoelectric device, and to adjust theinput power depending upon the temperature measurements. In an exampleembodiment, the temperature sensing devices include a first temperaturesensing device in thermal contact with one end of the thermoelectricdevice and a second temperature sensing device in thermal contact withan opposite end of the thermoelectric device. In an example embodiment,the temperature sensing devices include a first temperature sensingdevice in thermal contact with the interior chamber and a secondtemperature sensing device in thermal contact with an exterior portionof the housing. In an example embodiment, the electronics are configuredto estimate a rate of heat transfer based on the temperaturemeasurements. In an example embodiment, the temperature measurementsinclude an interior chamber temperature measurement, and the input poweris adjusted to maintain a functional relationship when the interiorchamber temperature measurement falls outside a range of acceptabletemperatures for a substance stored within the interior chamber. In anexample embodiment, the temperature measurements include an interiorchamber temperature measurement, and the input power is adjusted tomaintain a functional relationship when the interior chamber temperaturemeasurement falls inside a range of acceptable temperatures for asubstance stored within the interior chamber. In an example embodiment,the temperature measurements include an interior chamber temperaturemeasurement, and the input power is held substantially constant when theinterior chamber temperature measurement falls inside a range ofacceptable temperatures for a substance stored within the interiorchamber. In an example embodiment, the temperature measurements includean interior chamber temperature measurement, and the electronics areconfigured to apply the input power to cause the thermoelectric deviceto heat the interior chamber only when the interior chamber temperaturemeasurement indicates a dangerously cold condition for a substancestored in the interior chamber. In an example embodiment, thetemperature measurements include an interior chamber temperaturemeasurement, and the electronics are configured to apply the input powerto cause the thermoelectric device to cool the interior chamber at amaximum available cooling rate of the thermoelectric device only whenthe interior chamber temperature measurement indicates a dangerously hotcondition for a substance stored in the interior chamber.

In example embodiments, multiple different operating modes are availableand are selected (automatically, or otherwise) to accommodate normaloperating conditions or low energy reserve operating conditions.

Normal Operating Modes:

Example embodiments utilize a database of temperature ranges and/orother control parameters (as conceptually illustrated in Table 1 below).In an example embodiment, a set of temperature ranges is associated witheach different substance (drug, hormone, tissue, etc.) If the cold sidetemperature rises to “Dangerously Warm” levels where the cooled itembegins to thermally degrade, the controller will supply maximum coolinguntil the temperature drops into the “warm” range where thermaldegradation is minimal. Conversely, if the cold side temperature dropsdown to “Dangerously Cold” levels where freezing could destroy the item,the cooler will be operated as a heat pump that pumps heat from theoutside to the interior chamber to bring the temperature into the “cold”range. Operation as a heat pump requires reversing the polarity of thevoltage applied to the thermoelectric cooler. This can be accomplishedusing transistor switches, electromechanical relays, or through the useof a selectable second power converter with opposite output polarity.

TABLE 1 Example of Normal Operating Modes Danger- Danger- ously ouslyCategory Cold Cold Desired Warm Warm Condition: Potential Cooler thanOptimum Warmer Potential freezing desired than degrada- desired tionExample <32° F. >32° F. and >45° F. >55° F. >65° F. Range: <45° F. andand <55° F. <65° F. Action: Heating No cooling No net Moderate Maximumcooling cooling cooling

Example embodiments are directed toward maintaining the cooled item inthe “Desired” temperature range while consuming minimum power. Undernormal operating conditions, this is accomplished by providing moderatecooling when the item is in the “Warm” condition and no cooling in the“Cold” condition. The term “Moderate Cooling” refers to a cooling ratethat changes the internal cold side temperature by less than ˜10 degreesper hour. This results in thermal time constants of hours rather thanminutes for moving from the “Warm” or “Cold” condition to “Desired”.While higher levels of active cooling or heating could be used toquickly drive the temperature towards “Desired”, it has been observedthat this is less efficient than moderate levels of active cooling orheating. Use of long time constants effectively extends batterylifetime. The term “No net cooling” means the active heat transfer rateout of the cold side produced by the thermoelectric cooler matches theestimated heat transfer rate into the cold side by thermal conductionfrom the outside world. The term “No cooling” refers to thethermoelectric cooler being off.

In an example embodiment, the microcontroller first estimates the rateof heat transfer into the cold chamber based on the cold sidetemperature and the hot side temperature. The heat transfer rate isproportional to the temperature difference. The proportionality constantis determined by the physical geometry of the system and the materialsused. The microcontroller then calculates a required thermoelectricvoltage based on the estimated heat input and the cooling/voltagecharacteristic for the thermoelectric cooler with the measured hotside/cold side temperature difference. If the current temperature is inthe “Optimum” range, the microcontroller will output this voltage toproduce zero net cooling. The thermoelectric cooling rate will balancethe heat inflow rate. If the current temperature is in the “Warm” range,the microcontroller will output a slightly higher voltage to produceslight excess cooling with a slow drop in temperature over time. If thecurrent temperature is in the “Cold” range, the output voltage is 0; thethermoelectric cooler is turned off.

Low Energy Reserve Modes:

Use of a microcontroller with a battery voltage monitor allowsinitiation of emergency ultra-low power modes when the battery capacityhas been sufficiently exhausted. Battery voltage typically drops as thebattery capacity is used up, thus allowing battery voltage to serve as amonitor of remaining battery energy. A low-power indicator such as alight bulb, light emitting diode, liquid crystal display, audio orwireless alarm can be activated to alert the user that the batteries arenearing the end of their operating life and should be changed orrecharged. If the low battery warning is ignored and the battery voltagedrops further, the controller can shift emphasis from maintaining zerodegradation to minimizing thermal degradation as conceptuallyillustrated in Table 2 below. Under low energy reserve conditions,maximum heating or cooling rates are not used. Moderate heating/coolingrates are used to conserve power in the “Dangerously Cold/Warm”temperature ranges, and no net cooling is used in both the “Desired” and“Warm” temperature ranges. With further degradation in battery energyreserves, the controller will generate either no net cooling or zerocooling until the battery is exhausted.

TABLE 2 Example of Emergency Ultra-low-power Operating Modes Danger-Danger- ously ously Category Cold Cold Desired Warm Warm Condition:Potential Cooler than Optimum Warmer Potential freezing desired thandegrada- desired tion Example <32° F. >32° F. and >45° F. and >55°F. >65° F. Range: <45° F. <55° F. and <65° F. Action: Moderate Nocooling No net No net Moderate Heating cooling cooling or no net cooling

In an example embodiment, a refrigerator apparatus includes a housingwith an interior chamber, a thermoelectric device that is thermallycoupled to the interior chamber, temperature sensing devices thatprovide temperature measurements, and electronics configured to receivepower from a battery and to generate and apply input power to thethermoelectric device, and to adjust the input power according to anoperating mode selected by the electronics depending upon thetemperature measurements and a voltage measurement at an output of thebattery. In an example embodiment, the temperature sensing devicesinclude a first temperature sensing device in thermal contact with oneend of the thermoelectric device and a second temperature sensing devicein thermal contact with an opposite end of the thermoelectric device. Inan example embodiment, the temperature sensing devices include a firsttemperature sensing device in thermal contact with the interior chamberand a second temperature sensing device in thermal contact with anexterior portion of the housing. In an example embodiment, theelectronics are configured to estimate a rate of heat transfer based onthe temperature measurements. In an example embodiment, the temperaturemeasurements include an interior chamber temperature measurement, andthe input power is adjusted to maintain a functional relationshipbetween the input power and the interior chamber temperaturemeasurement. For example, the functional relationship includes aproportional relationship between the input power and the interiorchamber temperature measurement. In an example embodiment, thetemperature measurements include an interior chamber temperaturemeasurement, and the input power is adjusted to maintain a functionalrelationship when the interior chamber temperature measurement fallsoutside a range of acceptable temperatures for a substance stored withinthe interior chamber. In an example embodiment, the temperaturemeasurements include an interior chamber temperature measurement, andthe input power is adjusted to maintain a functional relationship whenthe interior chamber temperature measurement falls inside a range ofacceptable temperatures for a substance stored within the interiorchamber. In an example embodiment, the temperature measurements includean interior chamber temperature measurement, and the input power is heldsubstantially constant when the interior chamber temperature measurementfalls inside a range of acceptable temperatures for a substance storedwithin the interior chamber. In an example embodiment, the temperaturemeasurements include an interior chamber temperature measurement, andthe electronics are configured to apply the input power to cause thethermoelectric device to heat the interior chamber only when theinterior chamber temperature measurement indicates a dangerously coldcondition for a substance stored in the interior chamber. In an exampleembodiment, the temperature measurements include an interior chambertemperature measurement, and the electronics are configured to apply theinput power to cause the thermoelectric device to cool the interiorchamber at a maximum available cooling rate of the thermoelectric deviceonly when the interior chamber temperature measurement indicates adangerously hot condition for a substance stored in the interiorchamber. In an example embodiment, the operating mode is selected by theelectronics to be a normal operating mode when the voltage measurementindicates a sufficiently high battery output voltage, and a low energyreserve operating mode otherwise. For example, the electronics, whenadjusting the input power in the low energy reserve operating mode,prevent the thermoelectric device from operating at the maximum heatingor cooling rates of the thermoelectric device.

As noted above, example embodiments of the electronics include acommunications interface, which can be wireless or wired. In an exampleembodiment, the communications interface facilitates a radio connection(e.g., Bluetooth). In an example embodiment, the communicationsinterface includes a USB port. In an example embodiment, the electronicsare configured to receive data and/or control inputs via thecommunications interface.

In an example embodiment, the electronics are configured to draw powerfrom the communications interface. FIGS. 8 and 9 illustrate examples ofsuch electronics.

FIG. 8 shows an example embodiment of electronics 800 for a refrigeratorapparatus, the electronics including a Universal Serial Bus (USB)interface 340. FIG. 9 shows an example embodiment of electronics 900 fora refrigerator apparatus, the electronics including a USB interface 340and a battery charger 324. Electronics 800 and 900 are a simplifiedversion of the electronics 300, except as described differently below.

The USB interface 340 facilitates, inter alia, programming the coolerand/or downloading temperature data. In an example embodiment, themicrocontroller 304 includes digital input/output pins that can beconnected directly to the USB data lines. If the refrigerator apparatusis connected to a computer or powered USB hub by a USB cable, it canalso draw power from the computer or hub. USB cables have four wires: aground wire, a +5 V wire, and a twisted pair for data. The +5 V line cansupply up to 500 milliamperes. This +5 V line can be used to power theelectronics 800 and 900 for device programming or data readout.Recharging batteries requires additional battery charger circuitry. Tothis end, electronics 900 additionally include the battery charger 324configured as shown.

Although the present invention has been described in terms of theexample embodiments above, numerous modifications and/or additions tothe above-described embodiments would be readily apparent to one skilledin the art. It is intended that the scope of the present inventionextend to all such modifications and/or additions.

1. A refrigerator apparatus comprising: a housing with an interiorchamber; a thermoelectric device that is thermally coupled to theinterior chamber; a temperature sensing device that is thermally coupledto the interior chamber, the temperature sensing device providing atemperature measurement; and electronics configured to generate andapply input power to the thermoelectric device, and to adjust the inputpower maintaining a functional relationship between the input power andthe temperature measurement.
 2. The refrigerator apparatus of claim 1,wherein the functional relationship includes a proportional relationshipbetween the input power and the temperature measurement.
 3. Therefrigerator apparatus of claim 1, wherein the input power is adjustedto maintain the functional relationship when the temperature measurementfalls outside a range of acceptable temperatures for a substance storedwithin the interior chamber.
 4. The refrigerator apparatus of claim 1,wherein the input power is adjusted to maintain the functionalrelationship when the temperature measurement falls inside a range ofacceptable temperatures for a substance stored within the interiorchamber.
 5. The refrigerator apparatus of claim 1, wherein the inputpower is held substantially constant when the temperature measurementfalls inside a range of acceptable temperatures for a substance storedwithin the interior chamber.
 6. The refrigerator apparatus of claim 1,wherein no input power is applied when the temperature measurement fallsinside a range of acceptable temperatures for a substance stored withinthe interior chamber.
 7. The refrigerator apparatus of claim 1, whereinthe electronics are configured to apply the input power to cause thethermoelectric device to heat the interior chamber only when thetemperature measurement indicates a dangerously cold condition for asubstance stored in the interior chamber.
 8. The refrigerator apparatusof claim 1, wherein the electronics are configured to apply the inputpower to cause the thermoelectric device to cool the interior chamber ata maximum available cooling rate of the thermoelectric device only whenthe temperature measurement indicates a dangerously hot condition for asubstance stored in the interior chamber.
 9. The refrigerator apparatusof claim 1, wherein the temperature sensing device is a thermistorcircuit, and the electronics include a microcontroller that provides adigital output to activate the thermistor circuit.
 10. The refrigeratorapparatus of claim 1, wherein the electronics include a microcontrollerconfigured for direct connection to a battery without the use of avoltage regulator.
 11. A refrigerator apparatus comprising: a housingwith an interior chamber; a thermoelectric device that is thermallycoupled to the interior chamber; temperature sensing devices thatprovide temperature measurements; and electronics configured to generateand apply input power to the thermoelectric device, and to adjust theinput power depending upon the temperature measurements.
 12. Therefrigerator apparatus of claim 11, wherein the temperature sensingdevices include a first temperature sensing device in thermal contactwith one end of the thermoelectric device and a second temperaturesensing device in thermal contact with an opposite end of thethermoelectric device.
 13. The refrigerator apparatus of claim 11wherein the temperature sensing devices include a first temperaturesensing device in thermal contact with the interior chamber and a secondtemperature sensing device in thermal contact with an exterior portionof the housing.
 14. The refrigerator apparatus of claim 11, wherein theelectronics are configured to estimate a rate of heat transfer based onthe temperature measurements.
 15. The refrigerator apparatus of claim11, wherein the temperature measurements include an interior chambertemperature measurement, and the input power is adjusted to maintain afunctional relationship when the interior chamber temperaturemeasurement falls outside a range of acceptable temperatures for asubstance stored within the interior chamber.
 16. The refrigeratorapparatus of claim 11, wherein the temperature measurements include aninterior chamber temperature measurement, and the input power isadjusted to maintain a functional relationship when the interior chambertemperature measurement falls inside a range of acceptable temperaturesfor a substance stored within the interior chamber.
 17. The refrigeratorapparatus of claim 11, wherein the temperature measurements include aninterior chamber temperature measurement, and the input power is heldsubstantially constant when the interior chamber temperature measurementfalls inside a range of acceptable temperatures for a substance storedwithin the interior chamber.
 18. The refrigerator apparatus of claim 11,wherein the temperature measurements include an interior chambertemperature measurement, and the electronics are configured to apply theinput power to cause the thermoelectric device to heat the interiorchamber only when the interior chamber temperature measurement indicatesa dangerously cold condition for a substance stored in the interiorchamber.
 19. The refrigerator apparatus of claim 11, wherein thetemperature measurements include an interior chamber temperaturemeasurement, and the electronics are configured to apply the input powerto cause the thermoelectric device to cool the interior chamber at amaximum available cooling rate of the thermoelectric device only whenthe interior chamber temperature measurement indicates a dangerously hotcondition for a substance stored in the interior chamber.
 20. Therefrigerator apparatus of claim 11, wherein the electronics include amicrocontroller configured for direct connection to a battery withoutthe use of a voltage regulator.
 21. A refrigerator apparatus comprising:a housing with an interior chamber; a thermoelectric device that isthermally coupled to the interior chamber; and a temperature sensingdevice that is thermally coupled to the interior chamber, thetemperature sensing device providing a temperature measurement; andelectronics configured to receive power from a battery and to generateand apply input power to the thermoelectric device, and to adjust theinput power according to an operating mode selected by the electronicsdepending upon the temperature measurement and a voltage measurement atan output of the battery.
 22. The refrigerator apparatus of claim 21,wherein the operating mode is selected by the electronics to be a normaloperating mode when the voltage measurement indicates a sufficientlyhigh battery output voltage, and a low energy reserve operating modeotherwise.
 23. The refrigerator apparatus of claim 22, wherein theelectronics, when adjusting the input power in the low energy reserveoperating mode, prevent the thermoelectric device from operating at themaximum heating or cooling rates of the thermoelectric device.
 24. Therefrigerator apparatus of claim 21, wherein the operating mode includesa functional relationship between the input power and the temperaturemeasurement.
 25. The refrigerator apparatus of claim 24, wherein thefunctional relationship includes a proportional relationship between theinput power and the temperature measurement.
 26. The refrigeratorapparatus of claim 24, wherein the input power is adjusted to maintainthe functional relationship when the temperature measurement fallsoutside a range of acceptable temperatures for a substance stored withinthe interior chamber.
 27. The refrigerator apparatus of claim 24,wherein the input power is adjusted to maintain the functionalrelationship when the temperature measurement falls inside a range ofacceptable temperatures for a substance stored within the interiorchamber.
 28. The refrigerator apparatus of claim 21, wherein the inputpower is held substantially constant when the temperature measurementfalls inside a range of acceptable temperatures for a substance storedwithin the interior chamber.
 29. The refrigerator apparatus of claim 21,wherein the electronics are configured to apply the input power to causethe thermoelectric device to heat the interior chamber only when thetemperature measurement indicates a dangerously cold condition for asubstance stored in the interior chamber.
 30. The refrigerator apparatusof claim 21, wherein the electronics are configured to apply the inputpower to cause the thermoelectric device to cool the interior chamber ata maximum available cooling rate of the thermoelectric device only whenthe temperature measurement indicates a dangerously hot condition for asubstance stored in the interior chamber.
 31. A refrigerator apparatuscomprising: a housing with an interior chamber; a thermoelectric devicethat is thermally coupled to the interior chamber; temperature sensingdevices that provide temperature measurements; and electronicsconfigured to receive power from a battery and to generate and applyinput power to the thermoelectric device, and to adjust the input poweraccording to an operating mode selected by the electronics dependingupon the temperature measurements and a voltage measurement at an outputof the battery.
 32. The refrigerator apparatus of claim 31, wherein thetemperature sensing devices include a first temperature sensing devicein thermal contact with one end of the thermoelectric device and asecond temperature sensing device in thermal contact with an oppositeend of the thermoelectric device.
 33. The refrigerator apparatus ofclaim 31, wherein the temperature sensing devices include a firsttemperature sensing device in thermal contact with the interior chamberand a second temperature sensing device in thermal contact with anexterior portion of the housing.
 34. The refrigerator apparatus of claim31, wherein the electronics are configured to estimate a rate of heattransfer based on the temperature measurements.
 35. The refrigeratorapparatus of claim 31, wherein the temperature measurements include aninterior chamber temperature measurement, and the input power isadjusted to maintain a functional relationship between the input powerand the interior chamber temperature measurement.
 36. The refrigeratorapparatus of claim 35, wherein the functional relationship includes aproportional relationship between the input power and the interiorchamber temperature measurement.
 37. The refrigerator apparatus of claim31, wherein the temperature measurements include an interior chambertemperature measurement, and the input power is adjusted to maintain afunctional relationship when the interior chamber temperaturemeasurement falls outside a range of acceptable temperatures for asubstance stored within the interior chamber.
 38. The refrigeratorapparatus of claim 31, wherein the temperature measurements include aninterior chamber temperature measurement, and the input power isadjusted to maintain a functional relationship when the interior chambertemperature measurement falls inside a range of acceptable temperaturesfor a substance stored within the interior chamber.
 39. The refrigeratorapparatus of claim 31, wherein the temperature measurements include aninterior chamber temperature measurement, and the input power is heldsubstantially constant when the interior chamber temperature measurementfalls inside a range of acceptable temperatures for a substance storedwithin the interior chamber.
 40. The refrigerator apparatus of claim 31,wherein the temperature measurements include an interior chambertemperature measurement, and the electronics are configured to apply theinput power to cause the thermoelectric device to heat the interiorchamber only when the interior chamber temperature measurement indicatesa dangerously cold condition for a substance stored in the interiorchamber.
 41. The refrigerator apparatus of claim 31, wherein thetemperature measurements include an interior chamber temperaturemeasurement, and the electronics are configured to apply the input powerto cause the thermoelectric device to cool the interior chamber at amaximum available cooling rate of the thermoelectric device only whenthe interior chamber temperature measurement indicates a dangerously hotcondition for a substance stored in the interior chamber.
 42. Therefrigerator apparatus of claim 31, wherein the operating mode isselected by the electronics to be a normal operating mode when thevoltage measurement indicates a sufficiently high battery outputvoltage, and a low energy reserve operating mode otherwise.
 43. Therefrigerator apparatus of claim 42, wherein the electronics, whenadjusting the input power in the low energy reserve operating mode,prevent the thermoelectric device from operating at the maximum heatingor cooling rates of the thermoelectric device.
 44. The refrigeratorapparatus of claim 31, wherein the electronics include a microcontrollerconfigured for direct connection to the battery without the use of avoltage regulator.